This invention relates to a method of, and apparatus for, blow molding hollow articles of a thermoplastic material. More particularly, this invention relates to a method of, and apparatus for, blow molding hollow containers of a thermoplastic material.
The production of thermoplastic containers by shuttle blow molding is described, for example, in U.S. Pat. No. 3,614,807 (Lagoutte). In shuttle blow molding, two or more sets of blow molds, each of which is made up of a pair of mold halves that open and close relative to each other, are moved, in sequence, to engage an extruded tube of thermoplastic material at a moldable temperature, or a spaced apart plurality of such tubes in equipment used to simultaneously manufacture a plurality of containers in each mold set. Each mold set is then moved laterally away to a station where the portion of the tube in the mold set is blown into its desired configuration, as determined by the configuration of a cavity that is defined by the halves of the mold set, the lateral movement of each mold set often involving a first motion coaxial with the extruded tube to stretch the tube to properly size it and/or to axially orient material therein. The halves of the mold set are then opened to permit removal of the blown article, and the mold set is then returned to grasp another section of the extruded tube or tubes for a repeat of the process. The mold sets of a given shuttle blow molding machine move in predetermined paths relative to one another so that sequential portions of the-extruded tube are usually grasped by one or another of the mold sets, without the need to employ intermittent extrusion of the thermoplastic tube or tubes.
In the manufacture of containers by shuttle blow molding it has become popular to apply labels to the containers, by introducing a label or an opposed pair of labels into the open molds before the preforms or parisons are engaged thereby, by equipment that applies labels to the interiors of the open mold halves, and this equipment is generally described as in-mold labelling equipment. Known types of in-mold labelling equipment have the capacity to feed labels to the mold sets of a shuttle blow molding machine at a rate equal to the total of the production rates of all mold sets of the shuttle blow molding machine. Unfortunately, however, known types of shuttle blow molding machines position the various mold sets at different positions from one another while containers are being blown therein. This, then, requires an in-mold labelling machine for each mold set, notwithstanding that the total capacity of the multiple in-mold labelling machines for a given shuttle blow molding machine far exceeds the molding capacity of all the mold sets of the machines. The use of an in-mold labelling machine in connection with a shuttle blow molding machine is described, for example, in U.S. Pat. No. 4,769,205 (Oles et al.).
Another disadvantage of known types of shuttle blow molding machines that applies even when the machine is not being used to apply labels to the containers in the mold is that article removal equipment must be provided for each mold set, because the article removal positions of the various mold sets differ from one another.
Shuttle blow molding apparatus according to the present invention is made up of an extruder that continuously, vertically downwardly extrudes a tube, or a plurality of spaced apart tubes, or a blow head that continuously produces parisons of containers, along a vertically downwardly extending path. The extruded tube or parison is made up of thermoplastic material at a suitable temperature for blow molding into a useful article, or articles, such as a container, or containers, of the type used in a wide variety of packaging applications. The shuttle blow molding apparatus also includes pair of mold sets, or a superimposed plurality of pairs of mold sets, each set being made up of an opposed pair of mold halves that close and open with respect to each other, and the inside surfaces of the mold halves are configured so that the mold halves, when closed, define a cavity, or a plurality of cavities in the case of apparatus having a multi-tube extruder, in which an article is blown from a length of extruded tube to conform to the configuration of a cavity.
The shuttle blow molding apparatus of the present invention also includes apparatus for moving each mold set, in sequence, to an elevated position in which it grasps a length of extruded tube and then downwardly to permit another mold set to engage another length of extruded tube, with some stretching of the extruded tube, if desired, being done during the downward motion of a mold set. Preferably, the first mold set remains in engagement with the extruded tube until the second mold set engages the tube for controlled stretching of the tube for optimum material distribution and for more accurate positioning of the extruded tube until it is engaged by the second mold set.
In any case, after each mold set has reached a lower position, it is moved laterally, and preferably along a downward incline, to permit the section of the tube in the mold set, whose halves are now closed, to be blown into the intended article. At the conclusion of the blowing operation, the mold set, now no longer vertically aligned with the extruder, is moved upwardly to the elevation at which it will grasp another length of tube for a repeat of the cycle, but still out of vertical alignment with the extruder. At this position, the halves of the mold set are opened and the blown article(s) removed, whereupon the mold set is moved horizontally back to its start position to grasp another length of tube to begin a repeat of the cycle. In this manner, each mold set discharges molded articles at the same location, and only one set of take-off equipment is required for each multiple mold set shuttle blow molding apparatus.
When desired, a single in-mold labelling device may be used to apply labels to the interiors of the mold sets in which each of the parisons in a series are extruded before the parisons are blown into containers by the mold sets of a shuttle blow molding apparatus according to the present invention. In this case it is only necessary to begin the process with a slightly pre blown parison that is emitted by a die head into which compressed air, in addition to molten plastic, is introduced. Alternatively, the shuttle blow molding apparatus according to the present invention is adaptable to the manufacture of tandem containers in which each tandem is made up of a pair of containers, each of which is joined open end to open end, which is popular for the manufacture of relatively small containers, for example, six ounce containers. The shuttle blow molding apparatus according to the present invention is also adapted to the manufacture of large containers with integral handles, and it is adapted to the manufacture of containers with precisely calibrated, closure-receiving finishes.
Accordingly, it is an object of the present invention to provide an improved method of, and apparatus for, producing hollow articles of a thermoplastic material in multiple mold sets that move, in sequence, in closed paths relative to an extruder. More particularly, it is an object of the present invention to provide a method and apparatus of the foregoing character in which finished articles can be removed from each of the mold sets at only a single position. It is also an object of the present invention to provide a method and apparatus of the foregoing character in which labels can be applied to the interiors of open mold sets at a single location prior to the blowing of parisons into containers in the mold sets.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the invention and to the appended claims.